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Jun 27, 2018
06/18

by
E. Goldobin; D. Koelle; R. Kleiner

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We study a 0-$\pi$ dc superconducting quantum interference device (SQUID) with asymmetric inductances and critical currents of the two Josephson junctions (JJs). By considering such a dc SQUID as a black box with two terminals, we calculate its effective current-phase relation $I_s(\psi)$ and the Josephson energy $U(\psi)$, where $\psi$ is the Josephson phase across the terminals. We show that there is a domain of parameters where the black box has the properties of a $\varphi$ JJ with...

Topics: Condensed Matter, Superconductivity

Source: http://arxiv.org/abs/1504.05858

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0.0

Jun 30, 2018
06/18

by
Markus Thiemann; Daniel Bothner; Dieter Koelle; Reinhold Kleiner; Martin Dressel; Marc Scheffler

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Microwave spectroscopy is a powerful experimental tool to reveal information on the intrinsic properties of superconductors. Superconducting stripline resonators, where the material under study constitutes one of the ground planes, offer a high sensitivity to investigate superconducting bulk samples. In order to improve this measurement technique, we have studied stripline resonators made of niobium, and we compare the results to lead stripline resonators. With this technique we are able to...

Topics: Superconductivity, Condensed Matter

Source: http://arxiv.org/abs/1408.4727

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0.0

Jun 29, 2018
06/18

by
E. Goldobin; R. Menditto; D. Koelle; R. Kleiner

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We propose simple models for the current-voltage characteristics of typical Josephson ratchets. We consider the case of a ratchet working against a constant applied counter force and derive analytical expressions for the key characteristics of such a ratchet: rectification curve, stopping force, input and output powers and rectification efficiency. Optimization of the ratchet performance is discussed.

Topics: Mesoscale and Nanoscale Physics, Superconductivity, Condensed Matter

Source: http://arxiv.org/abs/1606.07371

3
3.0

Jun 28, 2018
06/18

by
E. Goldobin; S. Mironov; A. Buzdin; R. G. Mints; D. Koelle; R. Kleiner

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We consider a short Josephson junction with a phase discontinuity $\kappa$ created, e.g., by a pair of tiny current injectors, at some point $x_0$ along the length of the junction. We derive the effective current-phase relation (CPR) for the system as a whole, i.e., reduce it to an effective point-like junction. From the effective CPR we obtain the ground state of the system and predict the dependence of its critical current on $\kappa$. We show that in a large range of $\kappa$ values the...

Topics: Superconductivity, Condensed Matter

Source: http://arxiv.org/abs/1508.04317

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0.0

Jun 29, 2018
06/18

by
M. J. Martínez-Pérez; D. Gella; B. Müller; V. Morosh; R. Wöbling; J. Sesé; O. Kieler; R. Kleiner; D. Koelle

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We present the design, realization and performance of a three-axis vector nano Superconducting QUantum Interference Device (nanoSQUID). It consists of three mutually orthogonal SQUID nanoloops that allow distinguishing the three components of the vector magnetic moment of individual nanoparticles placed at a specific position. The device is based on Nb/HfTi/Nb Josephson junctions and exhibits linewidths of $\sim 250$ nm and inner loop areas of $600 \times 90$ nm$^2$ and $500 \times 500$ nm$^2$....

Topics: Superconductivity, Condensed Matter

Source: http://arxiv.org/abs/1604.07195

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1.0

Jun 29, 2018
06/18

by
M. J. Martínez-Pérez; B. Müller; D. Schwebius; D. Korinski; R. Kleiner; J. Sesé; D. Koelle

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We demonstrate the operation of low-noise nano superconducting quantum interference devices (SQUIDs) based on the high critical field and high critical temperature superconductor YBa$_2$Cu$_3$O$_7$ (YBCO) as ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have been patterned by focused ion beam milling. This allows to precisely define the lateral dimensions of the SQUIDs so as to achieve large...

Topics: Mesoscale and Nanoscale Physics, Superconductivity, Condensed Matter

Source: http://arxiv.org/abs/1610.09150

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0.0

Jun 29, 2018
06/18

by
Fabian Rudau; Raphael Wieland; Julian Langer; Xianjing Zhou; Min Ji; Nickolay Kinev; Luyao Hao; Ya Huang; Jun Li; Peiheng Wu; Takeshi Hatano; Valery Koshelets; Huabing Wang; Dieter Koelle; Reinhold Kleiner

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We used 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a $250 \times 70\,\mu\mathrm{m}^2$ intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power a hot spot forms in the stack. Resonant electromagnetic modes, oscillating either along the length ((0, $n$) modes) or the width (($m$, 0)...

Topics: Superconductivity, Condensed Matter

Source: http://arxiv.org/abs/1602.08966

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0.0

Jun 29, 2018
06/18

by
R. Menditto; H. Sickinger; M. Weides; H. Kohlstedt; D. Koelle; R. Kleiner; E. Goldobin

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We demonstrate experimentally the operation of a deterministic Josephson ratchet with tunable asymmetry. The ratchet is based on a $\varphi$ Josephson junction with a ferromagnetic barrier operating in the underdamped regime. The system is probed also under the action of an additional dc current, which acts as a counter force trying to stop the ratchet. Under these conditions the ratchet works against the counter force, thus producing a non-zero output power. Finally, we estimate the efficiency...

Topics: Exactly Solvable and Integrable Systems, Superconductivity, Condensed Matter, Nonlinear Sciences

Source: http://arxiv.org/abs/1607.07717

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1.0

Jun 30, 2018
06/18

by
F. Rudau; M. Tsujimoto; B. Gross; T. E. Judd; R. Wieland; E. Goldobin; N. Kinev; J. Yuan; Y. Huang; M. Ji; X. J. Zhou; D. Y. An; A. Ishii; R. G. Mints; P. H. Wu; T. Hatano; H. B. Wang; V. P. Koshelets; D. Koelle; R. Kleiner

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We used one-dimensional coupled sine-Gordon equations combined with heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a $300\,\mu\mathrm{m}$ long intrinsic Josephson junction stack consisting of $N = 700$ junctions. The junctions in the stack are combined to $M$ segments where we assume that inside a segment all junctions behave identically. Most simulations are for $M = 20$. For not too high bath temperatures there is the appearence of a hot spot...

Topics: Superconductivity, Condensed Matter

Source: http://arxiv.org/abs/1412.0479

4
4.0

Jun 27, 2018
06/18

by
Tobias Schwarz; Roman Wölbing; Christopher F. Reiche; Benedikt Müller; Maria-José Martínez-Pérez; Thomas Mühl; Bernd Büchner; Reinhold Kleiner; Dieter Koelle

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We fabricated YBa$_2$Cu$_3$O$_7$ (YBCO) direct current (dc) nano superconducting quantum interference devices (nanoSQUIDs) based on grain boundary Josephson junctions by focused ion beam patterning. Characterization of electric transport and noise properties at 4.2$\,$K in magnetically shielded environment yields a very small inductance $L$ of a few pH for an optimized device geometry. This in turn results in very low values of flux noise $

Topics: Condensed Matter, Mesoscale and Nanoscale Physics, Superconductivity

Source: http://arxiv.org/abs/1503.06090